Aerobic, fed-batch fermentation is a common mode for the culture of industrially important microorganisms for the production of antibiotics, chemicals, biochemicals, enzymes, and other biologically derived products. This mode of operation entails, at the very least, feeding a carbon source to the culture, aeration, usually with air, and some means of mixing the culture to distribute substrate and disperse air bubbles. In most of the fermentation processes, the process requires a strong dispersion of micro-bubbles of air into the media, in order to permit transfer of oxygen and other gases from the bubbles to the micro-organisms.
In the case of stirred-tank reactors, mixing is provided by a combination of one or more impellers or turbines and induced gas circulation currents by the sparging of air into the reactor vessel. In the case of air-lift and bubble-column reactors, mixing is accomplished via the induced currents from the introduction of air into the reactor.
In all cases, gas-liquid mass transfer is a critical factor determining equipment and process performance. Processes that have high oxygen demand require powerful motors and compressors for mechanical agitation and delivery of air, respectively. Therefore, any factor that can make gas-liquid mass transfer more efficient is potentially beneficial because it reduces both variable costs and the capital expense of the reactor equipment.
This present invention provide methods, apparatuses and compositions that could reduce costs associated with oxygen transfer (e.g., electricity for air and mixing) in fermentation processes and/or allow fermentation vessels to operate at higher volumetric productivity. Any system that relies on a fermentation process that operates in a high oxygen transfer regime (e.g. Bacillus subtilis or Trichoderma fermentation processes) may potentially benefit from the methods, apparatuses and compositions described herein.